Optical coherence tomography (OCT) imaging systems having adaptable lens systems and related methods and computer program products

ABSTRACT

OCT imaging systems are provided for imaging a spherical-type eye including a source having an associated source arm path and a reference arm having an associated reference arm path coupled to the source path. The reference arm path has an associated reference arm path length. A sample is also provided having an associated sample arm path coupled to the source arm and reference arm paths. A lens having a focal power optimized for a diameter of the spherical-type eye is provided along with a reference arm path length adjustment module coupled to the reference arm. The reference arm path length adjustment module is configured to automatically adjust the reference arm path length such that the reference arm path length is based on an eye diameter of the subject.

CLAIM OF PRIORITY

The present application is a continuation of U.S. patent applicationSer. No. 12/429,323, filed Apr. 24, 2009 (now U.S. Pat. No. 8,783,866),which claims priority from U.S. Provisional Application No. 61/047,592,filed Apr. 24, 2008, the disclosures of which are hereby incorporatedherein by reference as if set forth in their entirety.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with government support under grant number2R44EY015585 awarded by National Institutes of Health, National EyeInstitute. The United States Government has certain rights in thisinvention.

FIELD

The present invention relates to imaging and, more particularly, tooptical coherence tomography (OCT) and related systems, methods andcomputer program products.

BACKGROUND

Spectral Domain (SD)-OCT provides real time images of surface andsubsurface structures. In the eye, for example, OCT can be used to imagethe cornea, the iris, the crystalline lens and the retina. Typically,the subject being imaged is a cooperative adult patient having theirhead positioned in a chin-rest before imaging the eye. The imagingoptics used are typically optimized for the human adult eye, andspecifically for imaging of the anterior segment of the eye, i.e., thecornea to the iris, or the posterior pole of the eye, i.e., the retina.In conventional systems, these distinct portions of the eye requireindependent optical imaging systems, and generally cannot be imagedusing the same optics. Furthermore, such systems are now commonlyconfigured with an iris camera, a fundus camera, or a scanning laserophthalmoscope (SLO) or line scanning ophthalmoscope (LSO), that providehigh speed photographic views of the respective features of the eye tofacilitate alignment of the OCT image, and a record of the location ofthe OCT image.

Not all subjects of interest are cooperative as the adult patient.Furthermore, not all subjects of interest have optical properties thatare similar or equivalent to the adult eye, or are even scaled versionsof the adult eye. For example, a rodent eye more closely approximates aspherical, or ball, lens. Imaging the retina of the rodent eye, foreither fundus photography, SLO or LSO imaging, or OCT, typicallyrequires objective optics specifically designed for these ball-lenssystems. Rodents are in an important class of subjects for pre-clinicalresearch that cannot be imaged in a typical clinical imaging appliancefor many reasons. For example, most rodents do not cooperate withchin-rest alignment systems. Yet rodent imaging is very important forresearch in ophthalmology and in research of systemic disease processesthat influence neurologic and vascular function. Rodents, for example,mice and rats, are very well suited models for evaluating biologicalfunction as wild-type, are well suited to genetic modification forevaluating specific genotypes and phenotypes, and provide excellentmodels for evaluating response to a wide variety of treatments.Accordingly, high resolution, high throughput imaging systems thatprovide the highest quality images of ocular structure in rodent modelsefficiently and reproducibly may be desired.

SUMMARY

Some embodiments of the present invention provide optical coherencetomography (OCT) systems for imaging an eye including a lens systemconfigured to adjust such that the lens system can image both anteriorand posterior regions of the eye without changing any lenses in the lenssystem.

In further embodiments of the present invention, the lens system mayinclude three lens complexes, each of the lens complexes including atleast one lens. The lens system may include first, second and thirdlenses. The first lens may be a collimator lens and have a focal lengthof f1; a distance D1A distal to the collimator lens may be agalvanometer configured to steer a light beam over a region of interestin the eye; the second lens may be a distance D1B distal from thegalvanometer and have a focal length f2; and a distance D2A distal tothe second lens may be a plane perpendicular to an optical axis dividinga distance D2 into two parts, the distance D2A and a distance D2B.

In still further embodiments of the present invention, the distance D1Band the distance D2A are approximately equal to the focal length f2 andthe distance D2B is variable. In certain embodiments, the distance D1Ais adjustable. The third lens may be an objective lens, has a focallength f3 and may be the variable distance D2B to the right of theplane.

In some embodiments, the system may further include a distance D_corneafrom the objective lens to an anterior surface of the cornea; a distanceD_pivot to a pivot point at a point optically conjugate to a position ofthe galvanometer, where scanning beams cross; and a distance D_focus inair where the optical beams are in focus. D_pivot may be approximatelyequal to the focal length f3 beyond the objective lens and whereindistance D_focus may be determined by the following lens formula:1/D2B+1/D_focus=1/f3, wherein the index of refraction of a media inwhich D2B and D_focus reside is approximately equal to 1.

In further embodiments of the present invention, the lens system mayhave a first configuration wherein the probe bore tip containing theobjective lens is extended to increase the distance D2B to a thresholdvalue. The threshold value may be determined using the lens formula toplace a distance D_focus at a proper distance from the objective lensfor imaging the cornea and to optimize a depth of focus to a desiredvalue for imaging the cornea.

In still further embodiments of the present invention, the lens systemmay have a second configuration wherein a handheld probe of the OCTsystem and the lens system is driven closer to the eye and wherein anoperator of the handheld probe slowly draws the probe bore tip toward anominal lens position, which shortens the distance D2B, lengthens adistance D_focus and keeps a distance D_pivot constant. The distance D2Bmay be between f3 and 2*f3 such that an anterior segment of the eyeprovides a portion of optical power used to focus an optical beam onintermediate structures of the eye.

In some embodiments of the present invention, the lens system may have athird configuration where a handheld probe of the OCT system is movedcloser to the eye and an operator of the probe contracts the probe boretip back to a nominal retina position, which occurs when D2B=f3 andcontinues moving the probe inward until a distance D_cornea isapproximately equal to a design working distance to the eye and adistance D_pivot places a pivot point in an iris plane.

In further embodiments of the present invention, a reference arm pathlength of the OCT system may be adjusted to accommodate subject eyelengths in a sample arm of the OCT system.

In still further embodiments of the present invention, a reference armpath length of the OCT system may be adjusted to accommodate subjectpath lengths to target structures within the eye, target structuresranging from anterior of the cornea to posterior of the retina. Anteriorto posterior structures of a spherical-type sample are imagedcontinuously by synchronous coordination of a working distance betweenan objective lens and an anterior surface of the sample, and thereference arm path length. The continuous anterior to posterior imagingmay be accomplished automatically using a data processing system,wherein the relationship between working distance and the reference armpath length is determined by a pre-defined function or look-up table.

In some embodiments of the present invention, the lens system may havean associated focus adjustment that enables the OCT system to be focusedbased on refractive correction.

In further embodiments of the present invention, the system may be awide field imaging system providing a field of view of about equal to orgreater than 50 degrees.

In still further embodiments of the present invention, the system may bea wide field imaging system providing a field of view of about equal toor greater than 140 degrees in combination with rotation about a pupil.

In some embodiments of the present invention, the OCT system may beportable such that the OCT system is provided to the subject where thesubject is located. The portable OCT system may be configured to provideimaging to a subject independent of the orientation of the subject. Theportable OCT system may include a video and/or digital fundus camera.

In further embodiments of the present invention, the portable OCT systemmay further include a foot pedal and/or finger trigger configured tocontrol focus adjustment, reference arm path length adjustment and/ortrigger acquisition of an image.

Still further embodiments of the present invention provided optical OCTimaging systems for imaging an eye, including optics configured to imagean eye having a spherical shape.

In some embodiments of the present invention, an amount of optical powerused to obtain an OCT image of the eye having a spherical shape is afunction of a spherical radius of the eye. The eye may be a rodent eye.

In further embodiments of the present invention, the system furthercomprises a telecentric lens that is a doublet pair configured to createa telecentric plane with a substantially flattened field curvature atthe telecentric plane. The doublet pair may yield a telecentric planehaving a field curvature radius of greater than about 100 mm.

In still further embodiments of the present invention, the system mayfurther include a focusing lens set configured to have substantiallygreater power to accommodate the spherical shaped eye. Power for a mousemay be about +80D and power for a rat having an eye diameter of about6.4 mm may be about 73 Diopters.

Some embodiments of the present invention provide methods for imaging anin eye using OCT system including imaging both anterior and posteriorregions of the eye without changing any lenses in the lens system.

Further embodiments of the present invention provide methods for imagingan eye in an OCT imaging system including imaging an eye having aspherical shape using optics configured to image spherical shapedobjects.

Still further embodiments of the present invention provide methods forimaging an eye in an OCT imaging system including imaging continuouslyfrom an anterior position of the eye to a posterior position of the eyeby synchronous coordination of a working distance between a lens and asample and a reference arm path length.

Some embodiments of the present invention provide computer programproducts for imaging in an eye using OCT systems including computerreadable storage medium having computer readable program code embodiedin said medium. The computer readable program code including computerreadable program code configured to image both anterior and posteriorregions of the eye without changing any lenses in the lens system.

Further embodiments of the present invention provide computer programproducts for imaging in an eye using OCT systems including computerreadable storage medium having computer readable program code embodiedin said medium. The computer readable program code including computerreadable program code configured to image an eye having a sphericalshape using optics configured to image spherical shaped objects.

Still further embodiments of the present invention provide OCT imagingsystems for imaging a spherical-type eye including a source having anassociated source arm path; a reference arm having an associatedreference arm path coupled to the source path, the reference arm pathhaving an associated reference arm path length; a sample having anassociated sample arm path coupled to the source arm and reference armpaths; a lens having a focal power optimized for a diameter of thespherical-type eye; and a reference arm path length adjustment modulecoupled to the reference arm, the reference arm path length adjustmentmodule configured to automatically adjust the reference arm path lengthsuch that the reference arm path length is based on an eye diameter ofthe subject.

In some embodiments of the present invention the reference arm pathlength is adjusted to accommodate subject eye diameters in the samplearm ranging from about 1.0 mm to about 15 mm.

In further embodiments of the present invention, a lens system includingat least one lens is provided in the sample arm path and at least onesurface of the eye, the lens system having a field curvature thatmatches a curvature of a retina of the spherical eye of the subject.

In still further embodiments of the present invention, the subject maybe a mouse, a rat or a macaque.

Some embodiments of the present invention provide optical imaging lensesfor imaging a back surface of a ball-lens subject or ball-lens type eyeincluding an achromatic doublet pair; and an optical power determinedfrom a function or table and corresponding to a diameter or curvature ofsubject surfaces, wherein the optical power is greater than or equal to+30D.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a Fourier domain retinal opticalcoherence tomography system in accordance with some embodiments of thepresent invention.

FIG. 2 is a block diagram illustrating a Fourier domain corneal opticalcoherence tomography system in accordance with some embodiments of thepresent invention.

FIG. 3 is a diagram illustrating an optical system for human retinalimaging in accordance with some embodiments of the present invention.

FIGS. 4A and 4B are diagrams illustrating focal conditions at aposterior pole of spherical eye in accordance with some embodiments ofthe present invention.

FIGS. 5A through 5C are diagrams illustrating focal conditions atposterior pole of spherical eye in accordance with some embodiments ofthe present invention.

FIGS. 6A and 6B are diagrams illustrating images of a rodent retina withadult human optimized optics with an additional positive power doubletpair in accordance with some embodiments of the present invention.

FIGS. 7A through 7C are diagrams illustrating imaging of an eye withtypical telecentric cornea imaging optics in accordance with someembodiments of the present invention.

FIG. 8 is a diagram illustrating high power non-telecentric imagingoptic for spherical objects in accordance with some embodiments of thepresent invention.

FIG. 9 is a diagram illustrating focal field curvature optimization toposterior pole radius of curvature of spherical eye in accordance withsome embodiments of the present invention.

FIGS. 10A through 10D illustrate sequential imaging with systems inaccordance with some embodiments of the present invention from thecornea to the retina.

FIGS. 11A through 11C illustrate positions for imaging cornea forlateral resolution in accordance with some embodiments of the presentinvention.

FIG. 12 is graph illustrating RMS spot size vs. angular field of view inaccordance with some embodiments of the present invention.

FIG. 13 is a graph illustrating Objective Power vs. Axial Length/SphereDiameter in accordance with some embodiments of the present invention.

FIG. 14 is a graph illustrating Path Length Increase vs. WorkingDistance Decrease Corresponding to Imaging structures from Anterior toPosterior in accordance with some embodiments of the present invention.

FIG. 15 is a graph illustrating Path Length Increase vs. WorkingDistance Decrease Corresponding to Imaging structures from Anterior toPosterior in accordance with some embodiments of the present invention.

FIG. 16 a table illustrating design prescription for mouse retinalimaging corresponding to the lens system of FIG. 8 and the mouse eyemodel of FIG. 9 in accordance with some embodiments of the presentinvention.

FIGS. 17A through 17C are diagrams illustrating three lens complexesincluding in OCT systems in accordance with some embodiments of thepresent invention.

FIG. 18 is a block diagram of a data processing system suitable for usein some embodiments of the present invention.

FIG. 19 is a more detailed block diagram of a system according to someembodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention will be described more fully hereinafter withreference to the accompanying figures, in which embodiments of theinvention are shown. This invention may, however, be embodied in manyalternate forms and should not be construed as limited to theembodiments set forth herein.

Accordingly, while the invention is susceptible to various modificationsand alternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that there is no intent to limit theinvention to the particular forms disclosed, but on the contrary, theinvention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims. Like numbers refer to like elements throughout the descriptionof the figures.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”,“comprising,” “includes” and/or “including” when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof. Moreover, whenan element is referred to as being “responsive” or “connected” toanother element, it can be directly responsive or connected to the otherelement, or intervening elements may be present. In contrast, when anelement is referred to as being “directly responsive” or “directlyconnected” to another element, there are no intervening elementspresent. As used herein the term “and/or” includes any and allcombinations of one or more of the associated listed items and may beabbreviated as “/”.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement without departing from the teachings of the disclosure. Althoughsome of the diagrams include arrows on communication paths to show aprimary direction of communication, it is to be understood thatcommunication may occur in the opposite direction to the depictedarrows.

Conventional imaging systems do not provide high quality images ofspherical eyes found in, for example, rodents. As discussed above, thecapability of imaging spherical rodent eyes may be very important toclinical research. Accordingly, some embodiments of the presentinvention provide imaging systems that provide high quality imaging ofposterior imaging structures of animal models with ball-lens ocularphenotypes. In some embodiments, these imaging systems of allow imagingof both anterior structures and posterior structures of the eye withoutchanging the imaging lenses in the system.

In some embodiments of the present invention, imaging systems areconfigured to provide a continuous view of structures from the anteriorof the cornea through the posterior, or outer layers, of the retina tothe extent of optical translucency, as a simple function of relativeposition of the imaging lens to the eye of the subject, for example, bychanging the working distance.

In some embodiments of the present invention, the imaging system can beapplied to photographic, SLO or LSO, or OCT images of the structures ofthe subject model.

In some embodiments of the present invention, an optical prescription isprovided for this optical system that provides for optimal lateralresolution in the imaging of the posterior pole of the subject eye.

In some embodiments of the present invention, an optical prescription isprovided for this optical system that provides for optimal matchingbetween the field curvature of the focal plane at the retina of thesubject eye with the curvature of the retina of the subject.

In some embodiments of the present invention, an optical prescription isprovided for this optical system that provides for optimal imaging ofthe retina of a subject having a ball-lens phenotype, whereby theprescription scales with the diameter of the subject eye.

In some embodiments of the present invention, a prescription foralignment and imaging of these subject models is provided that includesobserving an image acquired as the imaging lens is brought intoincreasingly close proximity to the subject eye by observing orientationof the structural features of the subject eye as a function of depth.

In some embodiments of the present invention, a prescription is providedfor alignment and imaging of these subject models that includesmodifying alignment of the optical system in response to feedback fromthe observation of the image acquired as the imaging lens is broughtinto increasingly close proximity to the subject eye by observingorientation of the structural features of the subject eye as a functionof depth.

In some embodiments of the present invention, a prescription foroptimizing the quality and performance of an OCT imaging system isprovided by adjusting the reference arm length in coordination with thesample arm length of the interferometric imaging system in a continuousmanner as the imaging system is positioned for imaging structures fromthe anterior of the cornea through to the posterior of the retina.

In some embodiments of the present invention the OCT imaging ofarbitrary structures through a ball-lens optic is provided.

The adult human eye is a very capable imaging system. The emmetropichuman eye focuses distant objects at the retina, using the refractivepower of the cornea and the ocular lens. Close subjects are focused onthe retina by accommodation of the lens, a process that may degrade withage, i.e, presbyopia. The typical human subject requires some degree ofexternal correction for imperfect refractive properties of the eye. Amyopic, or near-sighted, subject, tends to focus distant objects infront of the retina, and corrective lenses with negative optical power,is required for normal vision. Conversely, a hyperopic, or far-sighted,subject tends to focus distant objects behind the retina, and mayrequire corrective lenses with positive power for normal vision. Imagingsystems that image the retina therefore generally are designed to imagethe emmetropic human eye, with a range of focal corrections from +12Diopter to −12 Diopter, and up to +/−20 Diopters.

Referring now to FIG. 1, a block diagram illustrating a Fourier domainretinal OCT system in accordance with some embodiments of the presentinvention will be discussed. As illustrated in FIG. 1, the systemincludes a low coherence source 100, a reference arm 300 and a samplearm 400 coupled to each other by a beamsplitter 200. The beamsplitter200 may be, for example, a fiber optic coupler or a bulk or micro-opticcoupler without departing from the scope of the present invention. Insome embodiments, the beamsplitter 200 may provide from about a 50/50 toabout a 90/10 split ratio. As further illustrated in FIG. 1, thebeamsplitter 200 is also coupled to a frequency sampled detection module600 over a path 605 that may be provided by an optical fiber.

As further illustrated in FIG. 1, the source 100 is coupled to thebeamsplitter 200 by a source path 105. The source 100 may be, forexample, an SLED or tunable source. The reference arm 300 is coupled tothe beamsplitter over a reference arm path 305. Similarly, the samplearm 400 is coupled to the beamsplitter 200 over the sample arm path 405.In some embodiments of the present invention, the source path, thereference arm path and the sample arm path may all be provided byoptical fiber.

In accordance with some embodiment of the present invention, thereference arm 300 further includes a collimator assembly 310, a variableattenuator 320 that can be neutral density or variable aperture, amirror assembly 330, a reference arm variable path length adjustment 340and a path length matching position 345, i.e. optical path lengthreference to sample. As further illustrated, the sample arm 400according to some embodiments of the present invention may include adual-axis scanner assembly 410 and an objective lens variable focus 420.

The sample in FIG. 1 is an eye 500 including a cornea 510, iris/pupil520, ocular lens 530 and eye length 540. As will be discussed in detailherein, the eye length in accordance with some embodiments of thepresent invention may be a subject specific, age dependent, pathologydependent axial optical eye length. As further illustrated in FIG. 1, arepresentation of an OCT imaging window 700 is illustrated near the eye500. As will be discussed further below, the retinal imaging systemrelies in the optics of the subject eye 500 to image the posteriorstructures of the eye.

FIG. 2 is a block diagram illustrating a Fourier domain (FD) cornea OCTsystem in accordance with some embodiments of the present invention. Asillustrated therein, the system of FIG. 2 is very similar to the systemof FIG. 1. However, the objective lens variable focus is not included.The anterior imaging system of FIG. 2 images the anterior structuresdirectly, without reliance on the optics of the subject to focus on theanterior structures.

It will be understood that the refractive properties of the subject eyedo impact the imaging, and such refractive properties may be accountedfor in quantitative image correction as discussed in U.S. Pat. No.7,072,047 to Westphal et al. Furthermore, imaging of intermediatestructures, including the ocular lens, may be accomplished withappropriately designed optics. In many cases, interference, and thusimaging, is achieved in FDOCT image systems over a range of depthsdefined by an optical path-length matched condition between a referencereflection and backscattering from structures in the sample, bound bythe ability to resolve high frequency components in a resultant spectralinterferogram. Imaging conditions for FDOCT, includingspectrometer-based (SDOCT) and swept-source-based configurations, arewell known in the art.

Referring now to FIG. 3, a diagram illustrating a representative imagingsystem for adult human retinal OCT will be discussed. A sample armsignal is transferred by optical fiber to the scanning imaging system400. The scanning imaging system may include the sample arm 400 andscanner assembly. The broadband light from the fiber is collimated 403,delivered to a 2-axis galvometric scanning system 410 (dual-axis scannerassembly), and imaged to telecentric imaging plane 435 with lens doublet430. The telecentric imaging plane 435 has a field radius of curvature,for example, of 16 mm, and is a conjugate to the input optical fiber.The scanning system sweeps a beam across this telecentric plane, whichis subsequently imaged to the retina using objective lens set 440 (lensdoublet pair) and the optics of the eye. An important attribute of theretinal imaging system is the existence of a pivot point 445 that isconjugate to galvometric scanners. At the pivot plane 445, thetelecentric scanning at 435 is converted into a sweeping scan that mapsof a field of view of the retina. Vignette-free imaging is achieved bylocating the pivot point 445 nominally within the pupil of the subjecteye. A well-design imaging system can image without dilation of the eye,though dilation reduces sensitivity to the placement of the pivot point,a key aspect to accurate subject position and thus image quality. In theemmetropic imaging condition, the scanned rays that are the image of theinput fiber at plane 435 are collimated by the lens set 440. The beamsdo not focus, but sweep out an angular pattern in the far field 450,pivoting around the galvo conjugate point 445. The far field 450 may bea radial-telecentric image plane, which is conjugate to the telecentricimage plane 435 and has a field radius of curvature in air of about 7.1mm. Optical power can be added or subtracted to correct for hyperopia ormyopia by modifying the separation of the lenses in the lens set 440.

Referring now to FIGS. 4A and 4B, diagrams illustrating focal conditionat posterior pole of a spherical eye, such as a mouse eye, in accordancewith some embodiments of the present invention will be discussed. Theimaging in FIG. 4 was modeled using human optimized optics as in FIG. 3,with emmetropic (zero Diopter) correction, shown as a function ofworking distance between the lens 440 and the cornea 510 of the rodenteye. The rodent eye is not well modeled as a scaled version of the humaneye. The rodent eye is very nearly a spherical, or ball lens asillustrated in FIGS. 4A and 4B. The rodent eye 500 has similarstructures to the human eye, including cornea 510, vitreous humor 515,pupil 520, lens 530, and retina 550. However, the shape of the cornea510 and lens 530 are much more spherical. FIGS. 4A and 4B illustrate thecapability of the emmotropic adult human optics illustrated in FIG. 3 toimage the rodent eye (spherical eye) of FIG. 4. The diagrams of FIG. 4actually model the eye of a mouse having a diameter of 3.2 mm. FIG. 4Aillustrates the bundle of scanned rays 437 imaged to the retina with thepivot point 447 positioned within the pupil 520. The rays 451 are unableto focus at the retina. On a human eye, the on-axis rms spot size forthe emmetropic subject is about 4.5 In the mouse model, the spot sizewith these optics is 39 μm. Improvement might be anticipated byincreasing the working distance between objective optics and subject,thus, moving the pivot point outward. However, the spot size onlyimproves to about 38.8 μm, and the field of view is constrained.Vignetting becomes a significant problem. This problem is not adequatelyaddressed by adding focusing power to the adult-optimized optics.

As illustrated in FIG. 5 the focusing on the rodent retina is notsubstantially improved by increasing the optical power of the of thehuman-optimized objective lens from 0 Diopter illustrated in FIG. 5A, to+20 Diopter illustrated in FIG. 5B (the extent of typical clinicalretinal OCT systems), or to +80 Diopter illustrated in FIG. 5C. As thepower is increased, the ball-lens optics makes it impossible to imagethe adult-optimized optics onto the retinal surface. Representativefocal points are highlighted as structures 453, 454 and 455,respectively.

In practice, it has been shown that some improvement can be achieved byadding an additional high power focusing optics between the adultimaging lens and the subject eye as illustrated, for example, in FIG.6A. An optimized auxillary doublet pair 800 improves focusing on theretina, yielding an on-axis rms spot of about 2.0 um. However, the pivotpoint is substantially broadened into a pivot area 448, cannot be driveninto the pupil, and the field of view is highly constrained, asdemonstrated by the RMS Spot Diameter vs. Field of View graphillustrated in FIG. 12. This solution is, however, much better than theuse of a single achromat solution most commonly applied. The singleachromat yields an on axis rms spot of about 30 μm.

It will be understood that an anterior imaging lens, and specifically acornea imaging lens, is nominally subject independent. A representativeanterior imaging optic is shown in FIG. 7A. A simple doublet 432 scanstelecentrically and focus at a prescribed working distance. The corneacan be imaged by placing the cornea at the appropriate focal workingdistance as shown in FIG. 7B. The rays 467 can focus anywhere in thecornea by adjusting the working distance, and the reference arm positionto maintain appropriate path-matching. This optic cannot image theretina, as all scanned rays focus in on one broad spot 457 as seen inFIG. 7C.

A solution to imaging the ball-lens phenotype of the rodent eye inaccordance with some embodiments of the present invention is illustratedin FIG. 8. The basic elements are shared in common with the humanimaging system: collimator, scanning galvos, telecentric lens, andfocusing optics. The optics are substantially redesigned and optimizedfor imaging through spherical media. The telecentric lens 434 is adoublet pair, creating a telecentric plane with a substantiallyflattened field curvature at the telecentric plane 435. This doubletpair consists of two 100 mm focal length lenses, and yields atelecentric plane with a field curvature radius of 103 mm, as comparedto the field curvature of a single achromat lens in a similarconfiguration of 16 mm. The focusing lens set 442 is pre-set to havesubstantially greater power in order to accommodate the ball-lens of thesubject. For the mouse, two 25 mm focal length achromats are set fornominal power of +80D. The separation between the galvos 410 and theproximal doublet pair 434 is 50 mm. The proximal doublet pair isseparated from the distal doublet pair 442 by 65 mm. For the rat, withan eye diameter of 6.4 mm, the nominal power of the lens set 442 is 73.3Diopters. The nominal design power scales inversely with lens diameter,owing to the curvature of the anterior surface that controls the bulk ofthe imaging power of the subject. The graph in FIG. 13 of objectivepower vs. Axial length/sphere diameter illustrates the nominal designpower as a function of optical axial length.

Imaging capability of systems in accordance with some embodiments of thepresent invention in the mouse eye is demonstrated in FIG. 9. Referringto FIG. 9, the input rays 437 are focused at the retinal plane 550, witha field curvature described by surface 452. The focal field curvature inthis case is 1.35 mm, which compares favorably with the retinal radiusof curvature 1.64 mm. The on-axis rms spot size is 1.2 um. The graph ofFIG. 12 shows the rms spot size as a function of scan angle,demonstrating a 50 degree field of view. The OCT imaging window isdefined by matching the reference arm path length to an effectiveoptical path length equivalent to the distance to a chosen surfaceanterior to the retina 345, and described by a FDOCT window 700. It isknown in the art that it may be desirable to invert the imaging window,placing the path-matching position 345 posterior to the retina; this maybe done without loss of generality. Furthermore, the optical systemspecifics given here for mouse models may be generalized to other rodentmodels or any other subject that is reasonably modeled as a ball-lensoptical system without loss of generality. The specific optical designprescription for the mouse model imaging is tabulated in Table 1 set outin FIG. 16.

The pre-focusing attribute of imaging systems in accordance with someembodiments of the present invention has advantages over therepresentative adult eye imaging system. In particular, systems inaccordance with some embodiments of the present invention allow imagingof all structures of the subject eye from anterior cornea through to theposterior retina without changing lenses by controlling the workingdistance between the imaging system and the eye and by coordinating thepath length matching condition by adjusting the reference arm pathlength.

FIGS. 10A through 10D illustrate sequential imaging with systems inaccordance with some embodiments of the present invention from thecornea to the retina. As illustrated in FIG. 10A, the system is focusedon the cornea, with the path length match position 348. As the workingdistance is reduced, the focus is translated to the anterior of theocular lens, with the path length position 347 illustrated in FIG. 10B.The working distance is further reduced to image the posterior lens, asshown in FIG. 10C, with the path length match position at 346. Finally,the retina is imaged in FIG. 10D, with path length match condition 345.The relative optical path length vs. imaging position is illustrated ina graph in FIG. 14.

The optimum position for imaging any structure in the eye is a functionof focus, location of the focus relative to a surface, and location ofthe reference path matching position to the focus. Optical systems inaccordance with some embodiments of the present invention are optimizedfor the retina, in the sense that the field curvature at the retinamatches the curvature of the retina. The field curvature does not matchthat of the all the other ocular structures, so it is desirable to setthe imaging conditions for optimum imaging of the desired structure.Most notably, it is often desirable to have high resolution, lateral andaxial, images of the cornea. Axial resolution in OCT is primarily afunction of the source bandwidth and not the delivery optics, but axialresolution may be impaired when lateral resolution is poor, as theinterferometric signal is intensity-weighted over the lateral spot.Accordingly, it may be useful to position the focus for optimal lateralresolution.

FIGS. 11A through 11C illustrate various positions for focal placementto image the cornea. The field curvature of the optical system isinverted with respect to that of the cornea, as, in fact, the rays aredivergent as they enter the cornea. Three locations for focal placementare at the anterior surface of the cornea (FIG. 11A); posterior surfaceof the cornea (FIG. 11B); and posterior to the cornea (FIG. 11C). Theoptimal on-axis lateral resolution is achieved by placing the focalposition at the anterior surface or posterior surface for concentrationon these surfaces, respectively. The optimal uniformity of lateralresolution across a field of view is achieved by placing the focusposterior to the cornea.

In all of the cases illustrated in FIGS. 11A through 11C, fromoptimizing the imaging of the cornea to imaging any structure through tothe retina, it is desirable to optimize the reference arm to maintainthe path-matching condition. Optical systems in accordance with someembodiments of the present invention not only provide optimal imaging ofspherical ocular systems, but uniquely enable automated sequentialwhole-eye imaging in a series of volumetric slices. The system mayreadily be set to image on the anterior-most surface, with appropriatefocus, working distance, and reference arm position. The relationshipbetween working distance decrease and reference arm path length increaseis non-linear, as shown in FIGS. 14 and 15. The acquisition may then beautomated to collect a series of whole-body volumes without manualintervention by simply coordinating the reduction in working distancewith the reference arm length according to a functional relationship orlook-up table as described above. At current image acquisition speeds of20,000 lines per second, high density images of 512×512×512 pixels maybe acquired, processed and displayed in 13 seconds. A mouse or rat eyemay be imaged in 3 sequential volumes offset by 1-2 mm (subjectdependent) with significant content overlap in 40 seconds; the contentoverlap enabling volume registration and image stitching. In someembodiments, lower density images of 256×256×512 pixels may be imaged in3 seconds, with 3 sequential volumes acquired in 12 seconds. Withemerging devices, imaging speeds will most likely rapidly increase to100,000 lines per second or faster, enabling high density, highresolution anterior-to-posterior volumes in under 10 seconds fordramatic high-throughput high resolution imaging of ocular structuresfrom cornea to retina in one image.

Example functionality of systems in accordance with some embodiments ofthe present invention will now be discussed herein. In order to view theretina, the operator moves the handheld probe (portable OCT system) andlens bore closer to the eye of the patient, using the OCT image to guidethe process. Some embodiments of the present invention provide ascanning OCT probe which is “easy to drive” in that the operator canclearly see major intermediate structures, for example, ocularstructures-such as the cornea, iris, crystalline lens, and finally theretina as he “drives” in toward the object of interest. In contrast tothe fixed lens system described above, a variable system offers certainimproved imaging attributes for optimizing anterior imaging andsubsequently optimizing posterior imaging. This is achieved bycontrolling certain optical distances in the system by extending orcontracting the probe bore.

OCT systems have been designed, manufactured and deployed for diagnosisof eye disease in patient populations with refractive errors rangingfrom myopia or nearsightedness, to emmetropia or no refractive error, tohyperopia or farsightedness. The greatest difficulty in using OCTsystems clinically is often the difficulty the operator has in obtaininga high quality image of the structure of interest, which may be theretina, for example, in patients with macular degeneration or glaucoma,the iris and crystalline lens, for example, in patients with cataract orother lens defects, or the cornea, for example, in refractive surgerypatients. Much of the intuition one develops in using “standard camera”(noninterferometric) optics, breaks down or is incomplete when usinginterferometrically based optical systems, such as OCT. In particular,the need to simultaneously achieve both good optical focus andappropriate reference arms length as the operator is searching forvisible landmarks in the eye can be daunting. Some embodiments of thepresent invention separate changes in focus from changes in optical pathlength, which determines the reference arm length required. This maygreatly simplify the use of the portable OCT systems (handheld probe) inaccordance with some embodiments of the present invention.

In particular, OCT systems in accordance with some embodiments of thepresent invention have three lens complexes, each of which may be madeup of one or more lenses. Three lens complexes according to someembodiments of the present invention are illustrated in FIGS. 17Athrough 17C. Referring first to FIG. 17A, from left to right, the firstlens 1780 is called the collimator lens with focal length f1. At adistance D1A to the right of the collimator lens 1780 are a galvanometeror galvanometer pair (galvos) 1781 which steer (or scan) the light beamover the region of interest. Assuming the light is well collimated, thedistance D1A is a free parameter whose value does not typically affectthe geometrical optical performance of the system and, may thus begoverned by other considerations such as mechanical constraints orcontrol of the optical path length through the system. At a distanceD1B=f2 from the galvanometers(s) is the second lens 1782 with focallength a A distance D2A=f2 to the right of the second lens 1782 is aplane Plane A perpendicular to the optical axis dividing the distance D2into two parts: D2A, which is approximately equal to f2, and D2B whichis variable. In each of the configurations discussed below, the systemto the left of Plane A is unchanged, i.e. D1A may be freely adjusted,and D1B and D2A are kept constant at f2. The third lens 1783 called theobjective lens has a focal length f3 and is a variable distance D2B tothe right of Plane A. To the right of the objective lens 1783 in the“open air”, i.e. outside the bore, are several distances of interest.The distance from the objective lens 1783 to the anterior surface of thecornea D_cornea, the distance to the “pivot point” D_pivot at a pointoptically conjugate to the position of the galvanometers 1781, where thescanning beams cross, and the distance, in air, i.e. not affected by theoptics of the eye, D_focus where the optical beams are in focus.

Using a first order analysis; second and higher order effects due toaberrations, for example, small changes in D_pivot and D_focus due tochanges in D2B will be ignored. To first order, distance D_pivot will beapproximately f3 beyond lens 3, and distance D_focus can be determinedby the following lens formula:1/D2B+1/D_focus=1/f3  Equation 1This formula assumes that the index of refraction of the media in whichD2B and D_focus reside is equal to 1, i.e. in air.

Operations of a portable OCT system (handheld probe in accordance withsome embodiments of the present invention will be discussed with respectto FIGS. 17A through 17C. Referring first to FIG. 17B (configuration 1),to begin imaging the eye, the operator extends the probe bore tipcontaining the objective lens 1783 by, for example, clockwise (CW) orcourter clockwise (CCW) twisting or linear braked friction extension, orother control to a hard stop, which increases the distance D2B to athreshold or maximum value. This value can be determined based on thelens formula set out in Equation D1 above to place D_focus at aconvenient distance from lens 3 or objective lens 1783 for imaging thecornea and also to optimize the depth of focus to a desired value whichis appropriate for the cornea. As illustrated in FIG. 17B, settingD2B=2*f3, for example, sets D_focus=2*f3 as well. This nominal “cornea”setting is appropriate for viewing the anterior surface of the cornea orany other structure whose surface is to be examined in air, after whichthe operator will be ready to “drive” the handheld probe inward tovisualize deeper structures as discussed further below.

Referring now to FIG. 17C (configuration 2), as the operator drives theprobe inward, i.e. moves the handheld probe and lens closer to the eyeof the patient, the operator slowly draws the probe bore tip toward thenominal “lens” position, which shortens D2B and lengthens D_focus, whileD_pivot remains constant. However, the optical power of the cornea nowadds additional positive focusing power which shortens the physicaldistance to the focus until it is located approximately at the iris andcrystalline lens of the eye. This corresponds to D2B between f3 and2*f3, for example, 1.5*f3 as illustrated in FIG. 17C. At this point, theanterior segment of the eye, particularly the cornea, provides part ofthe optical power required to focus the optical beam on the intermediatestructures, such as the iris and crystalline lens.

Referring again to FIG. 17A (configuration 3), this is the configurationfor collecting images of the retina. As the operator moves the probecloser to the eye, the operator also contracts the probe bore tip backall the way to the nominal “retina” position, which occurs when D2B=f3,and continues moving in until D_cornea equals the design workingdistance to the eye and D_pivot places the pivot point in the iris planeso that it will be minimally vignetted while the focus scans over thesurface of the retina. This position setting can also incorporate someadditional adjustment providing additional excursion in D2B toaccommodate a range of refractive errors in subjects. For example, whenD2B is approaching, but still greater than f3, the scanning beam exitinglens f3 will still be converging and will thus focus correctly on theretina in eyes which are too short, or hyperopic. This is theappropriate setting for mice which tend to have severely hyperopic eyes.When D2B=f3, this is the correct setting for emmetropic eyes. Byallowing D2B to be adjusted to values less than f3, this willaccommodate myopic eyes. Calibrated diopter settings can be labeled orengraved on the probe bore so that accurate diopter values can be dialedin for subjects with known refractive error.

A major benefit of handheld probes in accordance with some embodimentsof the present invention is that it is at least partly self compensatingin optical path length, i.e. as the probe is advanced from corneal tolens to retinal focus, the probe itself is shortened as D2B ranges fromD2B=˜2*f3, to f3<D2B<2*f3, to D2B=˜f3, thus the decreasing optical pathlength of the probe is compensated by the increasing pathlength in themedia of the eye, so that the overall optical path length may bedesigned to be relatively constant during this process. This is of greatbenefit in OCT, where changes in the optical path length of the sampleprobe can cause instabilities in the position of the OCT image in theavailable depth viewing range. In fact this condition of zero pathlength variation can be taken as a design parameter to optimize therange over which D2B can be adjusted. In some embodiments, if this isnot practical or desired, alternative means may be provided foradjusting the optical path length of other segments of the sample orreference arm, such as changing distance D1A in the probe or changingthe reference arm length via standard means, to allow for maintenance ofconstant optical path length difference between the arms as the probebore is extended and contracted. This can be done by, for example,monitoring the position of the probe bore through a mechanicaldisplacement or rotation sensor, using image processing to monitor theposition of some feature of the OCT image in axial length, or throughother means without departing from the scope of the present invention.

Thus, according to some embodiments of the present invention is may bemuch easier to obtain high resolution depth-resolved images of retinaland other ocular pathologies over a broad field of view in patients witha wide range of refractive errors and a wide range of ocular axiallengths. Finally, since the accommodative state of the lens may changeduring the exam, which is largely independent of axial length, there isa need to easily correct focus independent of reference arm length.

As discussed above, some aspects of the present invention may beimplemented by a data processing system. Exemplary embodiments of a dataprocessing system 1830 configured in accordance with embodiments of thepresent invention will be discussed with respect to FIG. 18. The dataprocessing system 1830 may include a user interface 1844, including, forexample, input device(s) such as a keyboard or keypad, a display, aspeaker and/or microphone, and a memory 1836 that communicate with aprocessor 1838. The data processing system 1830 may further include I/Odata port(s) 1846 that also communicates with the processor 1838. TheI/O data ports 1846 can be used to transfer information between the dataprocessing system 1830 and another computer system or a network using,for example, an Internet Protocol (IP) connection. These components maybe conventional components such as those used in many conventional dataprocessing systems, which may be configured to operate as describedherein.

Referring now to ′, a more detailed block diagram of a data processingsystem of FIG. 18 is provided that illustrates systems, methods, andcomputer program products in accordance with some embodiments of thepresent invention, which will now be discussed. As illustrated in FIG.19, the processor 1838 communicates with the memory 1836 via anaddress/data bus 1948, the I/O data ports 1846 via address/data bus 1949and the electronic display 1939 via address/data bus 1950. The processor1838 can be any commercially available or custom enterprise,application, personal, pervasive and/or embedded microprocessor,microcontroller, digital signal processor or the like. The memory 1836may include any memory device containing the software and data used toimplement the functionality of the data processing system 1830. Thememory 1836 can include, but is not limited to, the following types ofdevices: ROM, PROM, EPROM, EEPROM, flash memory, SRAM, and DRAM.

As further illustrated in FIG. 19, the memory 1836 may include severalcategories of software and data used in the system: an operating system1952; application programs 1954; input/output (I/O) device drivers 1958;and data 1956. As will be appreciated by those of skill in the art, theoperating system 1952 may be any operating system suitable for use witha data processing system, such as OS/2, AIX or zOS from InternationalBusiness Machines Corporation, Armonk, N.Y., Windows95, Windows98,Windows2000 or WindowsXP, or Windows CE or Windows 7 from MicrosoftCorporation, Redmond, Wash., Palm OS, Symbian OS, Cisco IOS, VxWorks,Unix or Linux. The I/O device drivers 1958 typically include softwareroutines assessed through the operating system 1952 by the applicationprograms 1954 to communicate with devices such as the I/O data port(s)1846 and certain memory 1836 components. The application programs 1954are illustrative of the programs that implement the various features ofthe some embodiments of the present invention and may include at leastone application that supports operations according to embodiments of thepresent invention. Finally, as illustrated, the data 1956 may includecaptured buffer data 1959 and streamed data 1960, which may representthe static and dynamic data used by the application programs 1954, theoperating system 1952, the I/O device drivers 1958, and other softwareprograms that may reside in the memory 1836.

As further illustrated in FIG. 19, according to some embodiments of thepresent invention, the application programs 1954 include OCT imagingmodules 1965. While the present invention is illustrated with referenceto OCT imaging modules 1965 as being application programs in FIG. 19, aswill be appreciated by those of skill in the art, other configurationsfall within the scope of the present invention. For example, rather thanbeing application programs 1954, these circuits and modules may also beincorporated into the operating system 1952 or other such logicaldivision of the data processing system. Furthermore, while the OCTimaging modules 1965 are illustrated in a single system, as will beappreciated by those of skill in the art, such functionality may bedistributed across one or more systems. Thus, the present inventionshould not be construed as limited to the configuration illustrated inFIG. 19, but may be provided by other arrangements and/or divisions offunctions between data processing systems. For example, although FIG. 19is illustrated as having various circuits, one or more of these circuitsmay be combined without departing from the scope of the presentinvention.

It will be understood that the OCT imaging modules 1965 may be used toimplement various portions of the present invention capable of beingperformed by a data processing system. For example, the OCT imagingmodules may be used to process and assess the images produced by the OCTsystem according to some embodiments of the present invention.

Example embodiments are described above with reference to block diagramsand/or flowchart illustrations of methods, devices, systems and/orcomputer program products. It is understood that a block of the blockdiagrams and/or flowchart illustrations, and combinations of blocks inthe block diagrams and/or flowchart illustrations, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, and/or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer and/or other programmable data processingapparatus, create means (functionality) and/or structure forimplementing the functions/acts specified in the block diagrams and/orflowchart block or blocks.

These computer program instructions may also be stored in acomputer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including instructions whichimplement the functions/acts specified in the block diagrams and/orflowchart block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer-implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions/acts specified inthe block diagrams and/or flowchart block or blocks.

Accordingly, example embodiments may be implemented in hardware and/orin software (including firmware, resident software, micro-code, etc.).Furthermore, example embodiments may take the form of a computer programproduct on a computer-usable or computer-readable storage medium havingcomputer-usable or computer-readable program code embodied in the mediumfor use by or in connection with an instruction execution system. In thecontext of this document, a computer-usable or computer-readable mediummay be any medium that can contain, store, communicate, propagate, ortransport the program for use by or in connection with the instructionexecution system, apparatus, or device.

The computer-usable or computer-readable medium may be, for example butnot limited to, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, device, or propagationmedium. More specific examples (a non-exhaustive list) of thecomputer-readable medium would include the following: an electricalconnection having one or more wires, a portable computer diskette, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,and a portable compact disc read-only memory (CD-ROM). Note that thecomputer-usable or computer-readable medium could even be paper oranother suitable medium upon which the program is printed, as theprogram can be electronically captured, via, for instance, opticalscanning of the paper or other medium, then compiled, interpreted, orotherwise processed in a suitable manner, if necessary, and then storedin a computer memory.

Computer program code for carrying out operations of data processingsystems discussed herein may be written in a high-level programminglanguage, such as Java, AJAX (Asynchronous JavaScript), C, and/or C++,for development convenience. In addition, computer program code forcarrying out operations of example embodiments may also be written inother programming languages, such as, but not limited to, interpretedlanguages. Some modules or routines may be written in assembly languageor even micro-code to enhance performance and/or memory usage. However,embodiments are not limited to a particular programming language. Itwill be further appreciated that the functionality of any or all of theprogram modules may also be implemented using discrete hardwarecomponents, one or more application specific integrated circuits(ASICs), or a field programmable gate array (FPGA), or a programmeddigital signal processor, a programmed logic controller (PLC), ormicrocontroller.

It should also be noted that in some alternate implementations, thefunctions/acts noted in the blocks may occur out of the order noted inthe flowcharts. For example, two blocks shown in succession may in factbe executed substantially concurrently or the blocks may sometimes beexecuted in the reverse order, depending upon the functionality/actsinvolved. Moreover, the functionality of a given block of the flowchartsand/or block diagrams may be separated into multiple blocks and/or thefunctionality of two or more blocks of the flowcharts and/or blockdiagrams may be at least partially integrated.

In the drawings and specification, there have been disclosed exemplaryembodiments of the invention. However, many variations and modificationscan be made to these embodiments without substantially departing fromthe principles of the present invention. Accordingly, although specificterms are used, they are used in a generic and descriptive sense onlyand not for purposes of limitation, the scope of the invention beingdefined by the following claims.

That which is claimed is:
 1. An optical coherence tomography (OCT)imaging system for imaging structures adjacent a posterior surface of asubstantially spherical ball-lens device, the system comprising: asource having an associated source arm path; a reference arm having anassociated reference arm path coupled to the source arm path, thereference arm path having an associated reference arm path length; asample arm having an associated sample arm path coupled to the sourcearm path, the sample arm comprising an input optical fiber deliveringoptical radiation from the source, at least one optical elementfollowing the input optical fiber, at least one scanning mirrorfollowing the at least one optical element, at least one optical elementfollowing the at least one scanning mirror, and the substantiallyspherical ball lens device following the at least one optical element; anon-zero working distance between the at least one optical element andthe substantially spherical ball lens device; and a reference arm pathlength adjustment module coupled to the reference arm, wherein theworking distance between the at least one optical element and thesubstantially spherical ball lens device are configured to adjust suchthat a conjugate of the at least one scanning mirror is imaged interiorto the substantially spherical ball lens device, posterior to theanterior surface of the substantially spherical ball lens device andanterior to the posterior surface of the substantially spherical balllens device; and wherein the optical radiation from the input opticalfiber is focused to an intermediate conjugate anterior to thesubstantially spherical ball lens device, wherefrom the intermediateconjugate of the optical radiation from the input optical fiber isfocused to a region posterior to the image of the at least one scanningmirror and to a region adjacent the posterior surface of thesubstantially spherical ball lens device.
 2. The OCT imaging system ofclaim 1, wherein the reference arm is adjusted in coordination with theworking distance to position an OCT image of the region adjacent theposterior surface of the substantially spherical ball lens device withina Fourier domain imaging window.
 3. The OCT imaging system of claim 1,wherein the optical radiation from the input optical fiber is focused toa substantially telecentric intermediate conjugate.
 4. The OCT imagingsystem of claim 1: wherein the at least one optical element within thesample arm has adjustable optical focusing power; and wherein theadjustable optical focusing power is controlled to adjust the positionof focus relative to the posterior surface of the substantiallyspherical ball lens device.
 5. The OCT imaging system of claim 4:wherein the at least one optical element within the sample arm hasadjustable optical focusing power; and wherein the adjustable opticalfocusing power is controlled to adjust the position of focus relative tothe posterior surface of the substantially spherical ball lens devicedependent on the diameter of the substantially spherical ball lensdevice.
 6. The OCT imaging system of claim 1: wherein the at least oneoptical element within the sample arm comprises at least oneinterchangeable element configured to adjust optical focusing power; andwherein the at least one interchangeable element is selected to adjustthe position of focus relative to the posterior surface of thesubstantially spherical ball lens device dependent on the diameter ofthe substantially spherical ball lens device.
 7. The OCT imaging systemof claim 1, wherein the substantially spherical ball lens device is adistal optical element in the sample arm of the OCT imaging system. 8.The OCT imaging system of claim 7: wherein the sample arm with thesubstantially spherical ball lens device is positioned proximate asubject under test; and wherein the structures adjacent the posteriorsurface of the substantially spherical ball lens device include thesubject under test.
 9. The OCT imaging system of claim 1, wherein thesubstantially spherical ball lens device is an element physicallyseparate from the sample arm of the OCT imaging system.
 10. The OCTimaging system of claim 9: wherein the substantially spherical ball lensdevice is proximate a subject under test; and wherein the structuresadjacent the posterior surface of the substantially spherical balldevice lens include the subject under test.
 11. The OCT imaging systemof claim 9, wherein the substantially spherical ball lens device is thesubject under test.
 12. A method for imaging structures adjacent aposterior surface of a substantially spherical ball lens device using ascanning optical coherence tomography (OCT) imaging system, the methodcomprising: positioning a substantially spherical ball lens devicedistal to sample arm optics of the scanning OCT imaging system;adjusting a working distance between the distal sample arm opticalelement and an anterior surface of the substantially spherical ball lensdevice such that a conjugate of at least one scanning mirror is imagedwithin the interior of the substantially spherical ball lens device,posterior to the anterior surface of the substantially spherical balllens device and anterior to the posterior surface of the substantiallyspherical ball lens device, such that a scanning beam pivots around aregion interior to the substantially spherical ball lens device; andfocusing optical radiation emanating from a distal end of an opticalfiber terminating in the sample arm to a region posterior to a positionof the conjugate of the at least one scanning mirror and to a regionadjacent the posterior surface of the substantially spherical ball lensdevice.
 13. A computer program product for imaging structures adjacent aposterior surface of a substantially spherical ball lens device using ascanning optical coherence tomography (OCT) system, the computer programproduct comprising: a non-transitory computer readable storage mediumhaving computer readable program code embodied in said medium, thecomputer readable program code comprising: computer readable programcode configured to image structures adjacent the posterior surface of asubstantially spherical ball lens device using optics positioned betweenat least one scanning mirror and the substantially spherical ball lensdevice, wherein the optics image are configured to image conjugate ofthe at least one scanning mirror to a region internal to thesubstantially spherical ball lens device and focus a light sourceposterior to the image of the at least one scanning mirror and to aregion adjacent the posterior surface of the substantially sphericalball lens device; and computer readable program code configured toprocess an optical coherence tomography image of a region adjacent theposterior surface of the substantially spherical ball lens device.